The present invention is related to railway tank cars and in particular to a protective structure for a manway or a valve-mounting nozzle on the top of a cargo tank of such a railway tank car.
Nozzles have long been provided on the top of a tank car as manways and for mounting valves used to fill a cargo tank with a fluid cargo, to remove the fluid cargo from the cargo tank, and to protect against excessive pressure. It has long been recognized that the nozzles are susceptible to being broken loose and that the valves can be broken in the event of a rollover of a railway tank car. Various protective housings have been designed, including containment caps for preventing loss of cargo in the event of accidents or failure of the valves. Various strengthened and reinforced nozzle structures have been provided in order to resist breakage of the nozzles in the case of a rollover, but previously known protective structures have failed when tank cars have overturned when moving at anything more than a minimal speed. For example, eight miles per hour may be a floor above which a significantly increased amount of protection for nozzles on the top of the cargo tank must be available in order to minimize risk of failure of a nozzle on the top of a cargo tank.
Cargo outlet valves are often provided on the bottom of a railway tank car, and it has been known to provide castings and other structures to surround such outlet valves and protect them in the event of a derailment of a tank car equipped with such a bottom valve. The bottom valves and their associated operating mechanisms, however, are significantly smaller than the manway and valve mounting nozzle structures typically found on the top of a railway tank car. While skid plates or castings have been used to protect the bottom outlet valves on railroad tank car cargo tanks, it had previously been considered unnecessary and an undesirable addition of weight to a railroad tank car to provide any such protective structure surrounding a manway nozzle or a valve group nozzle on the top of a railroad tank car, and, instead, welded gussets and various arrangements of strengthening of the attachment of a nozzle to the top of a cargo tank had been used in the past, as well as bells that can be attached to the valve group mounting plate to protect the valves themselves from damage in collisions and overturning. Known protective structures for a bottom valve do not appear to be able to be modified practically to provide the type of protection needed on the top of a railway tank car. Also, while previous protection for the top of a tank car has value, various events have recently proven that protection to be insufficient in the case of overturning of railroad tank cars in motion along a railroad track at a significant speed.
What is needed, then, is a substantial yet not overly massive structure for protecting the manway and valve mounting nozzles on the top of a cargo tank of a railway tank car, to prevent loss of cargo, and particularly to prevent escape of dangerous gaseous cargo or flammable liquid cargo, in the event of derailment and overturning of a railway tank car moving at a significant speed. Such a protective structure should not be so heavy as to add significantly to the fuel requirements for moving the car along the railway, yet it should be of ample strength. It is desirable also to have a nozzle on the top of a cargo tank be no larger than necessary, in order that it can provide a smaller target which can collide with an obstruction on the ground in the case of a rollover.
In one embodiment of the present invention, a protective structure for the top portion of a railway tank car may include elongate upstanding side members attached to the top of the cargo tank on each lateral side of the nozzles, supporting a skid having opposite end portions sloping upward from the top of the cargo tank to a central portion extending longitudinally above the manway or valve mounting nozzles.
In one embodiment, one or more transverse diaphragms may extend between the side members of the protective structure.
In one embodiment, a central portion of the skid may extend above the top portion of the cargo tank and define an access opening aligned with the nozzle, and there may be a cover plate selectively covering the access opening.
In one embodiment of the protective structure, valve operating mechanisms may extend laterally through openings defined in the side members of the protective structure, and the cover plate for the access opening may include a valve handle retainer to keep the valves on the nozzle in a closed condition.
The foregoing and other objectives, features, and advantages of the invention will be more readily understood upon consideration of the following detailed description of the invention taken in conjunction with the accompanying drawings.